HIGH-SPEED RAILWAY TRACKAlthough alternative track designs, such as paved track, havebeen developed, the majority of high-speed railway lines todayfeatures ballasted track. Over the past years, the laying andmaintenance methods for ballasted high-speed railway trackhave been optimised, making ballasted track a very economicalsolution with regard to life-cycle costs. The track of high-speedrailway lines requires a precise geometry, allowing only verytight tolerances that must be kept in the millimetre range, andmust be serviced accordingly from the outset. Neglect of main-tenance in the initial phase of the service life of high-speed rail-way track will cause inherent faults that cannot be compensatedlater.

Interaction between track and rolling stockTrack faults of different wavelengths stimulate railway vehiclebodies with different frequencies. Frequencies in the range ofbetween 0.5 and 10 Hz are regarded as critical for rolling stock.At lower speeds, these frequencies are caused by short-waveerrors, in which case it is sufficient to correct the track using thesmoothing method. However, at higher speeds, faults in trackgeometry with larger wavelengths also cause considerable dy-namic forces and must, therefore, be eliminated.

Fig. 1 shows that, at a speed of 160 km/h, faults withwavelengths of up to 100 m must be taken into considerationand that, at a speed of 350 km/h, even faults with a 200 mwavelength cause rolling stock reactions [1]. This correspondswith experience gained in practice by high-speed rail operatorsand has, recently, brought about a change in the trackmaintenance strategy adopted by some railways - changing fromthe smoothing method to the absolute track geometry method.

Absolute track geometry methodOn high-speed railway lines, deviations in track geometry fromthe target position have to be kept to a minimum. High-speedrailways, therefore, use absolute reference systems for trackgeometry.

In Austria and Germany, from 1972 onwards, fixed referencepoints were set up, generally on catenary masts, allowing theposition of the track to be defined in relation to the fixed pointsand the versines in between (Fig. 2). In other countries, e.g. theUnited Kingdom [2], France [3] and Switzerland, similarsystems have been introduced.

TRACK CONDITION MONITORING AND DIAGNOSISTrack condition monitoring of high-speed railway lines is a taskof major importance, in order to ensure ride quality and safety.

The basis of all track maintenance operations is an exactobservation and recording of the state of the track. On AustrianFederal Railways (ÖBB), for instance, this is carried out usingthe Plasser & Theurer EM 250 ([4], [5]) and EM 80 trackrecording cars. The core unit on the electronic track recordingcars of the EM series, which are available for various recordingspeeds and are in use on a great number of high-speed railwaylines, is the PAC (Plasser American Corp.) Non-contact InertialNavigational Track Geometry Measuring System with opticaldual-gauge measuring system (OGMS).

The PAC Inertial Navigational Track GeometryMeasuring System for accurate measurement resultsOn track recording cars for high-speed railway lines, non-contact track geometry measuring systems are used to enablehigh measuring speeds and ensure accurate and repeatablemeasuring results. For high-speed railway lines, it is importantto obtain information about both short-wave and long-wavedeviations in track geometry. Therefore, chord measuringsystems, which are based on a limited measuring length, havebeen replaced by inertial measuring systems that record aspatial curve. The PAC Inertial Navigational Track GeometryMeasuring System uses the Applanix POS/TG which, based ona three-dimensional laser gyroscope combined with GPSpositioning, delivers accurate position and orientation data forthe precise measurement of track geometry parameters (gauge,superelevation and calculated twist, longitudinal profile,horizontal alignment, curvature and grade), even at low speeds.

The core POS/TG system consists of an Inertial Measure-ment Unit (IMU) and a POS Computer System (PCS) withembedded Global Positioning System (GPS) receiver.

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Plasser & Theurer machines and technologies applied fortrack maintenance of high-speed railway lines: a selectionWhenever the speed or capacity of a railway line is increased, or a new high-speed railway line is built,the application of appropriate track maintenance procedures is very important to enable optimaland efficient use of these lines, as well as to maintain a high level of ride quality and safety. Trackmaintenance technologies are developed continuously to meet the demands of high-speed and high-capacity railway lines. This article looks at a selection of Plasser & Theurer machines and technologiesapplied for track maintenance of high-speed railway lines.

By: Ing. Rainer Wenty, Plasser & Theurer Export von Bahnbaumaschinen GmbH, Vienna, Austria.

Fig. 1: Reaction-oriented evaluation of track geometryat the critical frequency of 0.5-10 Hz

Fig. 2: Fixed-point reference system adopted on DB AG and ÖBB

Distance Measurement Indicator (DMI) and Optical GaugeMeasurement System (OGMS) sensors are used to provide thePOS/TG system with accurate data on distance travelled andhalf-gauge measurements.

Unlike vertical gyro-based systems, which are notorious forfalse orientation readings while subjected to centrifugal forcesduring turns, the POS/TG system provides the user with accu-rate track geometry output data under all dynamic conditions.During its operation, POS/TG constantly calibrates the inertialsensors of the IMU (three accelerometers and threegyroscopes) for improved track geometry and navigationperformance. This calibration and the nature of the trackgeometry computation algorithms implemented in POS/TGresult in the ability of the PAC Inertial Navigational TrackGeometry Measuring System to construct the track geometrymeasurements for a wide range of vehicle speeds.

The EM-SAT track survey carBefore any efficient and accurate track maintenance work canbe carried out, a survey of the actual track geometry has to bemade by measuring longitudinal level and alignment.

The EM-SAT track survey car (Fig. 3) enables fullymechanised measurement of the actual track geometry, using alaser reference chord. The EM-SAT consists of a main vehicle,equipped with a computer system and a laser beam receiver, andan auxiliary (“satellite”) trolley that carries a laser transmitter.Measurements are taken in a cyclic sequence. The machinemoves forward along a laser beam, emitted by the lasertransmitter on the satellite trolley. Any deviations from thetarget track geometry are measured and recorded. Every 50 to150 m, the satellite trolley stops at a fixed point and, then, movesforward again. The average measuring speed (including allstops) is 2.5 km/h.

Besides displacement and lifting values, superelevation andgauge faults can also be measured. The recorded data and thecalculated correction values are displayed on the computerscreen on-board the main vehicle, in a similar fashion as on theALC automatic guiding computer screen on-board the tampingmachine.

Electronic transmission of data to the tamping machineguarantees highest precision and, at the same time, prevents anytransmission faults that can occur in manual measuring.Experience gained on German Rail (DB AG) has shown anaccuracy of 1 mm, a measuring speed of 1.5 to 2.6 km/h, and acost reduction of EUR 3.00 per metre of measured track.

Satellite-supported track surveyingMaintaining fixed reference points is rather labour-intensiveand, therefore, quite costly. Furthermore, it is often found thattheir position has changed in the range of some centimetres.Also, manual measurement of the track position in relation tothe fixed reference points slows down the measuring speed, andis also a source of inaccuracy and further costs.

When building new lines, and when surveying existing lineswith regard to their general layout, the application of thesatellite-supported Global Positioning System (GPS) is alreadystandard technology.

The latest development now is the combined use of EM-SATand GPS (Fig. 4) to check the track geometry. The simultaneoussurveying of the actual track geometry using laser referencechords and GPS makes it possible to transmit the highlyaccurate laser reference chord data in absolute track co-ordinates.

Incorporation of a ballast profile measuring systemThe EM-SAT track survey car can further be equipped with anon-contact ballast profile measuring system, which records theballast profile by means of a laser scanner. The contour of theballast profile is computed from the sequence of pulses receivedand stored every 2 m (maximum speed 15 km/h). On thecomputer display, the measured profile is superimposed by theimage of the target profile appropriate to the line, which isselected by the operator at the start of work (Fig. 5). A surplus(green bars) or a lack of ballast (red bars) is indicated separatelyfor the left and right-hand side of the track, allowing the ballastprofile to be checked immediately during the measuring run.The recording results, which can be exported onto a disc or ZIPfor in-depth office evaluation, enable decisions to be madeabout the lifts to be performed and the ballast requirements.

EFFICIENT MAINTENANCE OFHIGH-SPEED RAILWAY TRACKThe maintenance of high-speed railway track requires a rangeof work processes that must be coordinated as efficiently aspossible. The better the work technologies act together, thehigher will be the achievable work output, the quality of workand, ultimately, the cost-efficiency.

The mechanised maintenance train (MDZ)Today, it is state-of-the-art in track construction and mainte-nance to use a group of machines - a high-capacity mechanisedmaintenance train (MDZ), the individual machines of which arematched in output, travelling speed and design parameters, thusforming a harmonic group of machines. MDZs are available indifferent levels of output; in each case, the tamping machineleads and determines the output (Fig. 6).

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Fig. 3: EM-SAT track survey car on Network Rail, United Kingdom

Fig. 4: Combined use of EM-SAT and GPS

Fig. 5: Computer display showing the measured ballast profilesuperimposed by the image of the target profile

To put a track into its correct geometrical position and toachieve a durable work result requires the following basicoperations:— track geometry correction, using a continuous-action levelling,

lining and tamping machine: in 1996, the continuous-actionthree-sleeper 09-3X Tamping Express was introduced onÖBB, which features a total of 48 tamping tines, arranged inpairs and interlaced, thus keeping the ballast penetrationreaction force to a minimum and enabling optimal squeezeoperation. The standard work technology of the 09-3XTamping Express is continuous-action three-sleeper tampingbut, at any time, the units can be changed to single-sleepertamping operation.

Using the 09-3X Tamping Express, which has a nominaloutput of 2,200 m/h, an increase in average daily output (shiftoutput) from 2.4 to 4 km has been observed on ÖBB, i.e. anincrease of around 42%. This means a much better utilisationof track possessions and, thus, a rise in the cost-efficiency ofmachine operation due to lower costs per unit of output.Since all its main lines have been maintained by three-sleepertamping machines, ÖBB also observed a substantial increasein track quality. The average track quality index has im-proved by 21%.

One of the latest machines for high-performance tampingis the 09-4X Dynamic Tamping Express continuous-actionfour-sleeper tamping machine with integrated dynamic trackstabilisation, which has a nominal output of 2,600 m/h;

— ballast profiling, using a ballast regulating machine: con-sidering that one kilometre of conventional double trackholds between 3,000 and 5,000 m3 of ballast (depending ontype and spacing of the track), the absolute necessity foreconomical handling and management of this valuable assetbecomes evident. Some sections of a track may lack ballast,while others have a surplus. So the goal has to be to regainthe surplus ballast and add it to where it is needed. Ballastregulating machines combine the task of ballast distributionand profiling.

Standard ballast regulating machines reshape the ballastbed by performing several runs backwards and forwards.However, with the development of continuous-actiontamping machines, it became necessary to re-design theballast regulating machines also.

Thus, “one pass” continuous-action ballast regulatingmachines, such as the USP series, featuring a ballast storagecapacity of 5-15 m3, were introduced. The machines arefitted with large-scale hoppers that enable a better distri-bution of the ballast and, thus, achieve savings in new ballast;

— final compaction and homogenisation of the ballast bed, usinga dynamic track stabiliser: ballast profiling is followed by trackstabilisation using a Dynamic Track Stabiliser (DTS), whichhas the task of re-stabilising the track following maintenance.This reduces the resistance to lateral displacement by around50%. Contrary to the natural settlement caused by trainloads, the application of the dynamic track stabiliseranticipates the initial settlements in a controlled mannerwithout altering the track geometry. After tamping work, thedynamic track stabiliser lowers the track as required,gripping the rail heads with roller clamps and setting thetrack into horizontal oscillation. At the same time, each railis pressed down in accordance with the readings of thelevelling device and the superelevation gauge.

The dynamic track stabiliser produces an uniform initialsettlement that is equal to a load of approx. 700,000 to800,000 tons. Thus, the range for further settlements isrestricted and the corrected track geometry is preserved forlonger. The result of this is an extension in maintenanceintervals of approx. 30%.

On German Rail (DB AG), a long-term trial to determinethe effect of dynamic track stabilisation on the developmentof track quality was conducted on a main-line track ofaverage condition near Regensburg [6]. After tamping, inSeptember 1999, the track quality was improved by around25%. In January 2001, i.e. 16 months later, the track sectionthat had been stabilised still showed an improvement of 21%,whereas the other track section that had not been stabilisedhad dropped to 8% improvement (Fig. 7); thus, a longerdurability of stabilised track is obvious.

Maintenance of high-speed switches and crossings usingthree-rail lifting and four-rail tamping machines (Fig. 8)The use of switch tamping machines featuring three-rail liftingand four rail-tamping ensures safe handling of high-speedswitches and improves the durability of track geometry cor-rection achieved [7].

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Fig. 6: High-capacity MDZ featuring a Tamping Express 09-3X as the lead machine

Three-rail liftingHeavier designs of switches and crossings, due tothe use of concrete sleepers and heavy railprofiles, demand additional measures for theirtreatment. When lifting such turnouts in thearea of the long sleepers, using the standardtwo-rail lifting unit, the reaction forces on therail fastenings exceed their yield strength. Thiswas first detected on DB AG and, therefore, anadditional lifting arm was developed for switchtamping machines [8]. Using this additionallifting arm, the diverging rail is liftedsimultaneously with the rails of the throughtrack, thus avoiding undue stress on railfastenings and sleepers. Today, three-rail liftingis a standard feature on switch tampingmachines. On most railways in Europe, three-rail lifting of turnouts featuring concretesleepers is mandatory.

Four-rail tampingIn addition to three-rail lifting, the introductionof four-rail tamping brought a furtherimprovement in the quality of switchmaintenance.

Fig. 7: Results of a track quality trial (with/without dynamic trackstabilisation (DTS)), conducted near Regensburg, Germany

The Unimat 08-475 4S, for instance, features four tampingunits. The outer units are mounted on telescopic arms, allowingthe tamping tools to reach a distance of 3,200 mm from the trackaxis. This enables both the through track and the diverging trackto be tamped in one operation. Thus, there is no danger that theswitch may tilt.

CONCLUSIONSIt is worthwhile investing in high-tech machines featuring soph-isticated work units. The output of the machines for track layingand maintenance has increased significantly and, more andmore, use is made of intelligent control circuits. This has adecisive effect on the cost-effective performance and the qualityof the work performed.

The focus is always on the long-term effect of a maintenanceoperation and, at the same time, optimisation of the costs.

As they ensure that a high level of maintenance is upheld,new high-technology machines contribute to the sustainabilityof the investments in high-speed railway lines.

REFERENCES[1] Haigermoser A.: ‘Demands of rolling stock on track quality’, Paper

presented to the Working Committee on Railway Technology(Infrastructure) of the Austrian Society for Traffic and TransportScience (ÖVG), 8 November 2004.

[2] Spoors R.: ‘Introduction of fixed point based track geometrymaintenance in the UK’, Rail Engineering International, Edition2004, Number 4, pp. 12-16.

[3] Le Bihan A.: ‘Track geometry maintenance on high-speed lines -SNCF’s experience’, Proceedings 15th International ÖVG Con-ference “Optimising the wheel/rail system - quality, cost efficiency &financing”, Salzburg, Austria, 14-16 September 2004.

[4] Presle G.: “The EM 250 high-speed track recording coach and theEM-SAT 120 track survey car as networked track geometrydiagnosis and therapy systems’, Rail Engineering International,Edition 2000, Number 3, pp. 14 and 15.

[5] Hanreich W.: ‘Modern permanent way inspection using the trackgeometry recording coach EM 250’, ZEVrail, September 2004, pp.18-27.

[6] Lichtberger B.: ‘Longer maintenance cycles achieved by DTS’, TrackCompendium, 2005, pp. 490-491.

[7] Lichtberger B.: ‘Careful and cost-effective installation, surveyingand tamping of high-capacity switches: a selection of Plasser &Theurer machines applied’, Rail Engineering International, Edition2004, Number 3, pp.11-14.

[8] Lichtberger B.: ‘Die neue Weichenstopftechnologie’, ETR-Eisenbahntechnische Rundschau, No. 11/1992, pp. 759-762.

Fig. 8: Tamping of a high-speed switch in France

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